Many cancers are characterized by disruptions in cellular signaling pathways that lead to aberrant control of cellular processes, or to uncontrolled growth and proliferation of cells. These disruptions are often caused by changes in the activity of particular signaling proteins, such as kinases. Among these cancers is non-small cell lung carcinoma (NSCLC). NSCLC is the leading cause of cancer death in the United States, and accounts for about 87% of all lung cancers. There are about 151,000 new cases of NSCLC in the United States annually, and it is estimated that over 120,000 patients will die annually from the disease in the United States alone. See “Cancer Facts and Figures 2005,” American Cancer Society. NSCLC, which comprises three distinct subtypes, is often only detected after it has metastasized, and thus the mortality rate is 75% within two years of diagnosis.
It is known that gene translocations resulting in kinase fusion proteins with aberrant signaling activity can directly lead to certain cancers. For example, it has been directly demonstrated that the BCR-ABL oncoprotein, a tyrosine kinase fusion protein, is the causative agent in human chronic myelogenous leukemia (CML). The BCR-ABL oncoprotein, which is found in at least 90-95% of CML cases, is generated by the translocation of gene sequences from the c-ABL protein tyrosine kinase on chromosome 9 into BCR sequences on chromosome 22, producing the so-called Philadelphia chromosome. See, e.g. Kurzock et al., N. Engl. J. Med. 319: 990-998 (1988). The translocation is also observed in acute lymphocytic leukemia and AML cases.
Gene translocations leading to mutant or fusion proteins implicated in a variety of other cancers have been described. For example, Falini et al., Blood 99(2): 409-426 (2002), review translocations known to occur in hematological cancers. To date, only a limited number of gene translocations and mutant proteins occurring in lung cancers have been described, including the t(15;19) translocation involving Notch3. See Dang et al., J. Natl. Can. Instit. 92(16): 1355-1357 (2000). Defects in RNA Binding Protein-6 (RBM-6) expression and/or activity have been found in small cell and non-small cell lung carcinomas. See Drabkin et al., Oncogene 8(16): 2589-97 (1999). However, to date, no translocations in human NSCLC cancer that involve protein kinases have been described.
CD74 is an integral membrane protein that functions as a MHC class II chaperone protein. Defects in ROS kinase expression resulting from the FIG-ROS del(6)(q21,q21) translocation in glioblastoma have been described. See Charest et al., Genes Chromos. Canc. 37(1): 58-71 (2003). A truncated form of ROS kinase able to drive tumor growth in mice has also been described. See Birchmeier et al., Mol. Cell. Bio. 6(9): 3109-3115 (1986). To date, there are no known activating point mutations that occur in ROS kinase.
Identifying translocations and mutations in human cancers is highly desirable because it can lead to the development of new therapeutics that target such fusion or mutant proteins, and to new diagnostics for identifying patients that have such gene translocations. For example, BCR-ABL has become a target for the development of therapeutics to treat leukemia. Most recently, Gleevec® (Imatinib mesylate, STI-571), a small molecule inhibitor of the ABL kinase, has been approved for the treatment of CML. This drug is the first of a new class of anti-proliferative agents designed to interfere with the signaling pathways that drive the growth of tumor cells. The development of this drug represents a significant advance over the conventional therapies for CML and ALL, chemotherapy and radiation, which are plagued by well known side-effects and are often of limited effect since they fail to specifically target the underlying causes of the malignancies. Likewise, reagents and methods for specifically detecting BCR-ABL fusion protein in patients, in order to identify patients most likely to respond to targeted inhibitors like Gleevec®, have been described.
Accordingly, there remains a need for the identification of novel gene translocations or mutations resulting in fusion or mutant proteins implicated in the progression of human cancers, including lung cancers like NSCLC, and the development of new reagents and methods for the study and detection of such fusion proteins. Identification of such fusion proteins will, among other things, desirably enable new methods for selecting patients for targeted therapies, as well as for the screening of new drugs that inhibit such mutant/fusion proteins.